Wis. Stat. § 75.13

If a proper affidavit of service of notice of application for tax deed or a proper proof of nonoccupancy, in due form, as provided in s. 75.12, has heretofore been filed with the county clerk, the fact that such affidavit of service of notice or affidavit of nonoccupancy or such proof has not been otherwise filed shall not be alleged or raised in any action or proceeding attacking or questioning the title of the county or its successors in interest in the land which was the subject of the notice or proof.